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Frequently Asked Questions

Q: When tracking, or slewing, OnStep pauses intermittently

A: Overheating. When the stepper driver overheats it temporarily shuts down, then restarts. This causes pauses in tracking during which time the stepper motor isn't energized.  Overheating is caused by the setting Vref being too high.  Vref should be set to give a current that matches your stepper motors within the stepper drivers' thermal and current limits.  More in this discussion as well as this message.

A: Insufficient power supply current.


Q: Tracking motion isn't smooth or "jumps" once every second or two

A: Zero-crossing "step-stuck" trouble which A4988's and DRV8825's sometimes have happen, search here in the group or google "step stuck.  Change the stepper drivers, change stepper motors, use the diode hack, or hack to switch to fast decay mode.  No guarantees that any of these will work or be acceptable (audible noise of fast decay, wasted power of diode hack, etc.)

A: Insufficient wire gauge to the stepper motors' can cause poor micro-stepping performance.

A: Vref set incorrectly (too low or too high.) Too low or high and the motor can cog to full step positions.


Q: How can I reset all the EEPROM values in OnStep?

A: You need to use the Arduino IDE and compile/upload a specific sketch. The exact sketch depends on the microcontroller you are using. For the Arduino Mega2560 you have to use the EEPROM Clear Sketch. For the STM32, you need the EEPROM Wipe sketch.


Q: Which Micro-controller option should I choose?

A: That depends on your budget and requirements.  The micro-controller you use can dictate what performance and limitations you will have with it.  In this section, we detail the major differences between different micro-controllers supported in OnStep.  Below is a breakdown of the performance and features for some commonly used options:

Micro-controller Performance Differences:
-----Board/Processor----- -----MCU~Speed---- ---Memory--- --Flash-- ---EEPROM/NV--- ---Hardware--- Timers --Hardware-- FP Math -Fastest*- Step Rate
MKS Gen-L/Mega2560 16 MHz 8K 256K 4K 3 x 16 bit No 31kHz
STM32/Bluepill 72 MHz 20K 128K 4K (on RTC) 3 x 16 bit No 80kHz
MiniPCB/Teensy3.2 72 MHz 64K 256K 2K 4 x 32 bit No 114kHz
MaxESP/ESP32 2 Core, 240 MHz 512K 4M 2K 2 x 32 bit Yes 100kHz
MaxPCB/Teensy3.5 120 MHz 192K 512K
4 x 32 bit
MaxPCB/Teensy3.6 180 MHz 256K 1M 4K 4 x 32 bit Yes 615kHz
Board/platform Features:
-----Board/Processor----- ----RTC---- --Encoder-- support --Focusers/-- Rotator --Stepper~Driver-- Mode Control
-TMC2130- Drivers Aux~I/O -Dew~Heaters~etc.**~ -Board+Processor- Approx. Cost
MKS Gen-L/Mega2560 DS3234+ + 3x On-the-fly+ Yes Many, 3x MOSFETs $20
STM32/Bluepill DS3231 + 1x On-the-fly Yes ? $20
MiniPCB/Teensy3.2 - + + On-the-fly Yes Aux0,1,2,3,4 $70
MaxESP/ESP32 DS3231 Built in 1x On-the-fly+ Yes Aux3,4,7,8 $70
MaxPCB/Teensy3.5,3.6 DS3231 Built in 2x On-the-fly Yes Aux0,3,4,7,8 $100

+ Means the feature can be added but it requires extra effort and might increase the difficulty of the build or otherwise has limitations.
* These figures assume a pulse wave form, square wave mode (the default) is 1.6x slower.  Where "on-the-fly" micro-step mode switching can be used the maximum goto speed is almost always limited by the motors/drive design not OnStep (even on a "slow" Mega2560.)
** Aux0 is normally the Status LED.  Aux1 & Aux2 are normally MISO for the TMC2130 (or for ESP-01 firmware upload control.)  Aux3 & Aux4 are normally for Home SW support.  If not used for the default these can be PWM (dew heater or screen for flats) or SW (OTA cover,) etc.  There are rules about which pins can do PWM not covered here.

Alignment Capabilities/Accuracy:

Note: the maximum alignment points and resolution are Goto Assist (GTA) limitations within the micro-controller only.  Sky Planetarium can be used on any Eq mode OnStep to perform the n-star alignment with up to 50 stars and 1 arc-second resolution.

Arduino Mega2560

Maximum number of alignment points: 6
Minimum alignment resolution 128 arc seconds

STM32 Blue Pill/Teensy 3.1/Teensy 3.2

Maximum number of alignment points: 6
Minimum alignment resolution 64 arc seconds


Maximum number of alignment points: 9
Minimum alignment resolution 16 arc seconds